Interesting bit that I worked out the other day that might be non-obvious for those not familiar with the demographics of Norway:
The 76 people that were killed in the attacks is a larger percentage of the country than the 4000 killed in the US on September 11th. So, despite the absolute numbers being far smaller, presumably the psychological impact is of a similar magnitude.
http://www.wolframalpha.com/input/?i=%2876+%2F+%28population...